The present invention relates to integrated circuit (IC) device assembly and, more particularly, to multi-die sensor devices.
A multi-die sensor device is a package incorporating multiple integrated circuit dies into a single package, at least one of which is a sensor die. The multiple dies assembled in one package usually are internally connected with wires. A multi-die sensor device performs all or most of the functions of an electronic system, and is widely used in electronic devices.
FIG. 1A is a cross-sectional view of a conventional multi-die sensor device 100 including a lead frame 102 having a flag 104 and a plurality of leads 106 surrounding the flag 104. First and second dies 108 and 110 are attached on a top surface of the flag 104. The first die 108 is electrically connected to at least one of the leads 106 with a first bond wire 112, and the second die 110 is electrically connected to the first die 108 with a second bond wire 114. In addition, a third die 116 is attached on a top surface of the first die 108 with an epoxy and electrically connected to the first die 108 with a third bond wire 118. The multi-die sensor device 100 may be, for example, a sensor device where the first die 108 is a micro-control unit (MCU), the second die 110 is a gravity sensor, and the third die 116 is a pressure sensor. The lead frame 102, the first and second dies 108 and 110, and the first and second bond wires 112 and 114 are encapsulated with a mold compound 120. Since the third die 116 is a pressure sensor die, an opening 122 should be left over the third die 116 so that it may function; however, the third die 116 is covered with a protective gel 124.
The opening 122 is created with a Film Assisted Molding (FAM) process in which an insert wrapped by a film is placed on top of the third die 116 to prevent the mold compound 120 from flowing into the area of the opening 122. However, there is a very narrow process tolerance since a minor offset of the FAM process will damage the first and second bond wires 112 and 114. Further, both insert and mold chase clamping pressures have very tight process windows in order to strike a balance between die cracking and mold bleeding.
FIG. 1B is a cross-sectional view of another conventional multi-die sensor device 200 including a substrate 202 having first and second dies 204 and 206 attached thereon. The first die 204 is electrically connected to a first bonding pad 208 on a top surface of the substrate 202 with a first bond wire 210. Both the first and second dies 204 and 206 are electrically connected to a second bonding pad 212 on the top surface of the substrate 202 respectively with a second bond wire 214 and a third bond wire 216 to electrically connect the second die 206 to the first die 204. A third die 218 is attached on a top surface of the first die 204 with an epoxy material and electrically connected to the first die 204 with a fourth bond wire 220. In the multi-die sensor device 200, the first die 204 is a MCU, the second die 206 is a gravity sensor, and the third die 218 is a pressure sensor. Part of the substrate 202, the second die 206 and the third bond wire 216 are encapsulated with a mold compound 222 through a pre-molding process, more particularly, a compression molding process. Since the third die 218 is a pressure sensor die, an opening 224 is left over top of the first and third dies 204 and 218 after the pre-molding process and then a gel 226 is disposed on a top surface of the third die 218. A lid 228 with a hole 230 is provided to cover the opening 224. However, there is a risk of damaging the diaphragm of the pressure sensor (third die 218) caused by the gel dispensing process. The height of the dispensing needle to the top surface of the third die 218 must be carefully controlled. Furthermore, a large amount of gel 226 is required to coat the first and third dies 204 and 218, and the bond wires 210, 214 and 220.
It is therefore desirable to find a solution to resolve the bond wires and the pressure sensor die protection issues in a sensor device.